Super Camouflage Beats Super Sight, But Only If You're A Fish

By Josh Davis

23 Aug 2016, 13:26

What would you rather have: super sight, or super camouflage? Well, it would seem that out in the ocean you’d do better to hide yourself, as new research suggests that the eyes of creatures that it was thought could see through the glamor of silvery fishes is nowhere near as effective as previously believed, and are actually no better than normal eyes in seeing long distance.

In general, when it comes to predators and prey, it is always better to see the other animal before they see you. This means that in the open ocean, where there is literally nothing to hide behind, pelagic fishes have developed a neat trick to make themselves disappear. By reflecting the light that makes it through the water with their silvery scales, fish such as herring, sardines, mackerel, and tuna are able to blend in seamlessly with the surrounding deep blue ocean.

But what it is thought they can’t hide is the polarized light that reflects off them, something which many predators, such as octopuses and squids (but not humans), have evolved to be able to see. This, it would therefore seem, is a perfect example of an evolutionary arms race, in which the prey develops a way to outfox the predators, and the predator counters it. But a new study published in Current Biology has tested this theory, by taking images of silvery fish using a custom-built camera that can detect polarized light.

What they found was that silvery fish could not be detected from a greater distance when using polarized light cues compared to using “regular” light cues such as brightness. This would seemingly be counterproductive if an animal has developed eyes that allow them to see polarized light to better help them hunt down hidden fishes. “There's a lot of polarized light underwater, and there are all these ocean animals that can see it, but we have no idea why,” says Sonke Johnsen, the first author of the study.

Interestingly, another study published recently has also looked into how these fishes remain hidden, and found that ocean going fish may have actually developed a way to conceal not just them themselves, but the polarized light reflected off them too. They researchers found that pelagic fishes have specially adapted blood cells that reflect the polarized light, and that these were more efficient when the fish are viewed at “chase angles”, those likely to be seen by predators as they hunt the prey.

So it would seem that Superman’s super vision might be no match for the Fantastic Four’s Invisible Woman, but only if they were underwater.